Vehicle floor structures have been known, for example, from Japanese Patent Application Laid-open Publication No. SHO-63-20284, where a floor section on which a vehicle occupant rests his or her feet during driving or the like is located at substantially the same height or level as footboards or steps (hereinafter referred to as “boarding steps”).
According to the disclosure in the No. SHO-63-20284 publication, a floor plate is provided between left and right side pipes constituting a main frame, and a step-mounting frame is secured to an outer side surface of each of the side pipes. Boarding step is secured to each of the step-mounting frames in such a manner that the floor plate and the boarding steps lie at substantially the same level. However, because the floor of the vehicle is formed by provision of the floor plate between the left and right side pipes, the disclosed floor structure can leave only a small space under the floor so that it is difficult to place component parts etc. of the vehicle in the under-floor space; generally, various harnesses, driving component parts, auxiliaries, etc. are placed in the under-floor space. If the under-floor space can be made greater, the above-mentioned component parts of the vehicle may be placed more easily in the under-floor space, and, besides, there may be secured an additional space for accommodating other small articles, which should achieve highly-enhanced convenience.
Further, vehicle body frame structures have been known, for example, from Japanese Patent Application Laid-open Publication No. HEI-1-164685, where suspension arms and suspension units are connected at their respective one ends to a frame member provided on a front portion of a vehicle body frame unit.
According to the disclosure in the No. HEI-1-164685 publication, a front body in the form of a thin press-formed plate, to which are secured upper and lower arms that support thereon a front wheel and suspension unit, is provided on a front frame constituting a front part of a front cage. Three brackets are provided on the front body, and one bracket is provided on a plate-shaped member constituting a lower tube that connects to a rear lower end portion of the front body. The upper arm is secured to one of the brackets on the front body, the lower arm is secured to another one of the brackets on the front body and to the bracket on the plate-shaped member, and the suspension unit is connected at its lower end to the upper arm. Respective assembly accuracy of the three brackets on the front body would considerably influence assembly accuracy of the upper and lower arms relative to a front axle and assembly accuracy of the suspension unit relative to the upper arm. Thus, if the assembly accuracy of the three brackets on the front body is lowered, then the assembly accuracy of the upper and lower arms and suspension unit would also be lowered. As a consequence, it tends to be difficult to manage the assembly accuracy of the brackets on the front body. Further, because the bracket on the plate-shaped member is separately provided from the front body, assembly accuracy between the font body and the plate-shaped member would also influence the assembly accuracy of the lower arm relative to the front axle, which tends to make the assembly accuracy management even more difficult. Further, from the viewpoint of the costs, it is desirable that the front body, to which the upper and lower arms and suspension unit are mounted, be simple in construction.